1. Field of the Invention
The embodiments discussed herein are related to a paper discharge device, and particularly to a technique for improving alignment of discharged paper sheets in the paper discharge device.
2. Description of the Related Art
With respect to a paper discharge device, a technique is proposed for preventing misalignment of discharged paper sheets when the paper sheets are stacked so that the discharged paper sheets are stacked on a paper discharge tray in an aligned state. For example, there is a paper discharge device that is configured so that the front end of a paper sheet to be discharged is placed on stacked paper sheets after coming into contact with the stacked paper sheets by making a discharge angle shallow. FIGS. 11A, 11B, 11C, 12A and 12B illustrate examples of such a paper discharge device. When contact between a paper sheet and discharge rollers is released and the paper sheet is discharged in a state in which the paper sheet is not in contact with stacked paper sheets, the paper sheet falls freely and reaches the stacked paper sheets. Then, positions of paper sheets that have reached the stacked paper sheets are dispersed, and as a result, alignment of discharged paper sheets deteriorates. Therefore, by discharging a paper sheet that is in contact with the stacked paper sheets and preventing the paper sheet from falling off, alignment of discharged paper sheets is prevented from deteriorating.
FIG. 11A is a diagram illustrating paper sheet discharge in a state in which there are no stacked paper sheets. A paper discharge device 100 includes a paper discharge tray 102 on which a discharged paper sheet 200 is stacked, and one discharge roller pair 104 that sandwiches the paper sheet 200 from above and below. Note that in regard to direction, in line with movement of the paper sheet 200 to be discharged, the leftward direction in the figure is referred to as the downstream direction and the rightward direction in the figure is referred to as the upstream direction.
The discharge roller pair 104 causes the paper sheet 200 to be discharged on the paper discharge tray 102 at such a discharge angle that the paper sheet is directed downward to the downstream side in the S direction. Then, the front end of the paper sheet 200 to be discharged begins to come into contact with the paper discharge tray 102 while the paper sheet 200 is conveyed by the paper discharge roller pair 104. Note that the discharge angle is determined by the angle of the paper discharge roller pair 104, etc.
FIG. 11B is a diagram illustrating paper sheet discharge in a state in which there are a few stacked paper sheets 210. In a state in which there are a few stacked paper sheets 210, the front end of the paper sheet 200 to be discharged is positioned at almost the same position as that in FIG. 11A, and begins to come into contact with the uppermost face of the stacked paper sheets 210. The distance between the contact start position and the front end position of the stacked paper sheets 210 is set to R. R is the contact length between the paper sheet 200 to be discharged and the uppermost face of the stacked paper sheets 210.
FIG. 11C is a diagram illustrating paper discharge in a state in which there are many stacked paper sheets 210. When the stacked amount (the number of stacked sheets) of the stacked paper sheets 210 increases, the contact start position of the front end of the paper sheet 200 to be discharged moves to an upstream side. That is, the contact length R becomes longer in comparison with that in a state in which there are fewer stacked paper sheets 210. When the stacked amount of the stacked paper sheets 210 increases, since the paper sheet 200 to be discharged is in contact with the uppermost face of the stacked paper sheets 210 for a longer time, the portion of the uppermost sheet of the stacked paper sheets 210 that is pushed out in the T direction by the paper sheet 200 to be discharged increases. Thus, alignment of discharged paper sheets deteriorates. As described, the paper discharge device 100 illustrated in FIG. 11C may prevent deterioration in alignment of discharged paper sheets due to falling-off of paper sheets; however, when there is a large stacked amount (number of stacked sheets), the paper discharger device 100 causes deterioration in alignment of discharged paper sheets due to pushing-out of paper sheets.
FIGS. 12A and 12B are diagrams illustrating how alignment of discharged paper sheets deteriorates when the size of the paper sheet 200 is large. For example, FIG. 12A illustrates a case in which the paper sheet 200 is A4 size (the size that is defined by ISO216, 210 mm×297 mm), and FIG. 12B illustrates a case in which the paper sheet 200 is A3 size (the size that is defined by ISO216, 297 mm×420 mm). When the paper sheet 200 is A3 size, the contact length R becomes longer and the contact time between the paper sheet 200 to be discharged and the uppermost face of the stacked paper sheets 210 becomes longer as compared with that when the paper sheet is A4 size. Therefore, even when the stacked amounts are the same, when the size of the paper sheet 200 becomes larger, alignment of discharged paper sheets deteriorates.
Although the paper discharge device 100 in which the contact start position moves to an upstream side when the stacked amount increases has been described in FIG. 11C, a paper discharge device 150 is proposed that is configured to lower the paper discharge tray 102 according to a stacked amount in order to stabilize the contact start position regardless of the stacked amount.
FIGS. 13A and 13B illustrate examples of the paper discharge device 150. FIG. 13A illustrates a state in which the stacked amount of the stacked paper sheets 210 is small, and FIG. 13B illustrates a state in which the stacked amount of the stacked paper sheets 210 is large. As illustrated in FIG. 13B, the paper discharge device 150 detects an increase in the stacked height of the stacked paper sheets 210 and lowers the paper discharge tray 102 using a motor or the like by the increased amount. Thus, the contact length R is made approximately constant regardless of the stacked amount of the stacked paper sheets 210, and deterioration in alignment of discharged paper sheets due to the influence of the stacked amount is prevented. An example of the paper discharge device configured to lower the paper discharge tray 102 is disclosed in Japanese Laid-open Patent Publication No. H10-246998.